Thermoplastic resins, typically polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, nylon, polyethylene terephthalate and polyethylene naphthalate have superior physical and chemical properties and are used for fibers, plastics, films, sheets, adhesives and the like. In recent years, antibacterial goods having an inorganic and/or organic antibacterial agent incorporated therein or applied thereto are becoming available in the market.
Main antibacterial agents currently under investigation or in use include natural antibacterial agents such as chitin, chitosan, wasabi extracts, mustard extracts, hinokitiol and tea extracts, inorganic compounds such as titanium oxide particles (catalytic in photooxidation), fine particles of zinc oxide, silver-containing zeolite and silver-containing zirconium phosphate, and synthetic antibacterial agents such as organic ammonium salt compounds and organic phosphonium salt compounds.
Natural antibacterial agents and inorganic antibacterial agents, typically silver, are now attracting attention in view of their safety from toxicity. The following inventions have been disclosed.
Japanese Unexamined Patent Publication No.83905/1991 discloses silver ion-containing phosphate-based antibacterial agents and Japanese Unexamined Patent Publication No.161409/1991 discloses an antibacterial agent wherein a specific volume of zeolite having a specific ion exchange volume is substituted with silver ions.
Films, sheets, fibers and plastics were prepared according to the techniques of these publications and were tested for antibacterial properties against Staphylococcus aureus, Escherichia coli and the like. The results show that if the antibacterial agent was used in a relatively small amount to retain the clarity of the moldings, the moldings showed a low degree of antibacterial activity. However, an improvement in antibacterial activity required sacrifice of clarity. Thus, it was found that the moldings disclosed in the publications remained to be improved for practical use.
On the other hand, synthetic organic antibacterial agents are generally superior in antibacterial activity against fungi compared with natural antibacterial agents and inorganic antibacterial agents. However, if the synthetic organic antibacterial agent is applied to the surface of a substrate such as a film or incorporated thereinto, the antibacterial agent is easily evaporated, released or separated from the surface of the substrate because the antibacterial agent is of low molecular weight. Hence, the application or incorporation of such antibacterial agent is undesirable in terms of prolonged stability of antibacterial activity and safety of human bodies.
When an antibacterial agent is used for a film or the like, it is desirable from the viewpoints of prolonged stability of antibacterial properties and safety of human bodies that the antibacterial agent be undissolved in water, an organic solvent or the like, becoming difficult to release, give off, peel or separate from the film surface. In such situation, recently an immobilized type of antibacterial agent was disclosed. The disclosed antibacterial agent contains an organic antibacterial agent attached, due to ionic bond or covalent bonding, to a polymer used as a raw material for films or fibers.
Japanese Unexamined Patent Publication No.86584/1979 discloses an antibacterial material predominantly comprising a high molecular substance which contains an antibacterial component having a quaternary ammonium salt group attached, due to ionic bond, to an acid group such as a carboxyl group or a sulfonic acid group. Japanese Unexamined Patent Publication No.245378/1986 describes fibers composed of a polyester copolymer containing an antibacterial component having a base group such as a amidine group and a quaternary ammonium salt group.
Phosphonium salt compounds are known as a biologically active chemical compound having a wide spectrum of activity against bacteria like various nitrogen-containing compounds, as disclosed in Japanese Unexamined Patent Publications Nos.204286/1982; 60903/1988; 114903/1987; 93596/1989; and 240090/1990.
Disclosed is an invention which attempts to extend the applications of said phosphonium salt by its immobilization to a polymer. Japanese Unexamined Patent Publication No.266912/1992 discloses a phosphonium salt-containing vinyl polymer as the antibacterial agent. Japanese Unexamined Patent Publication No.814365/1992 describes a vinylbenzyl phosphonium salt-containing vinyl polymer as the antibacterial agent. Japanese Unexamined Patent Publication No.310820/1993 teaches an antibacterial material predominantly comprising a high molecular substance which contains an antibacterial component having an acid group and a phosphonium salt group attached to the acid group due to ionic bond. Disclosed in Examples is a polyester prepared using a phosphonium salt of sulfoisophthalic acid.
Japanese Unexamined Patent Publication No.41408/1994 discloses a modified polyester and a film formed therefrom, the modified polyester comprising a polyester copolymer prepared from a phosphonium salt of sulfonic acid and polyalkylene glycol, the modified polyester being used as a support for photographic purposes, or usable for wrapping, for general industrial purposes or for magnetic tape, although without reference to the antibacterial activity thereof. The alkyl group attached to the phosphonium salt described in said patent specification includes, for example, a butyl group, a phenyl group and a benzyl group all of which have a relatively few carbon atoms, unlike the group disclosed in Japanese Unexamined Patent Publication No.310820/1993.
Based on Japanese Unexamined Patent Publications Nos.266912/1992; 814365/1992 and 310820/1993, a vinyl polymer containing a phosphonium salt group and a polyester (copolymer) were prepared according to Examples described in the publications, and were molded into fibers, films, sheets and the like. Then, fibers, films, sheets and the like were coated with the disclosed antibacterial polymer to provide a laminate. The antibacterial properties of the laminate were evaluated and found unsatisfactory. A polyester having at least 50 mole % of tri-n-butyldodecyl phosphonium salt group attached thereto was prepared in an attempt to improve the antibacterial properties, and was molded into films, sheets and the like. The moldings suffered insufficient antibacterial properties as well as colored polymers and lowered mechanical properties due to the drop of glass transition point.
Further, fibers, fabrics, films, sheets, plastics and the like were formed using said inorganic and organic antibacterial agents either singly or in combination and were tested for antibacterial properties against Staphylococcus aureus, Escherichia coli and the like. The moldings were found to have a low antibacterial activity and were unsuitable for use.